Year	Years
1970	4.94
1971	5.03
1972	5.12
1973	5.21
1974	5.31
1975	5.4
1976	5.49
1977	5.58
1978	5.67
1979	5.76
1980	5.85
1981	5.94
1982	6.03
1983	6.12
1984	6.2
1985	6.29
1986	6.37
1987	6.46
1988	6.54
1989	6.62
1990	6.69
1991	6.77
1992	6.84
1993	6.91
1994	6.98
1995	7.05
1996	7.15
1997	7.26
1998	7.37
1999	7.49
2000	7.6
2001	7.72
2002	7.84
2003	7.96
2004	8.08
2005	8.2
2006	8.33
2007	8.46
2008	8.58
2009	8.71
2010	8.84
2011	8.97
2012	9.1
2013	9.23
2014	9.37
2015	9.5